This invention relates to a door latch assembly and relates particularly to a spindle adapter which is mounted on a spindle for operating a latch bolt and further to a locking mechanism for selectively preventing operation of the latch bolt.
In a typical door-mounted latch arrangement, a spindle extends from within an outside latch operator, such as knobs, handles, levers and the like, through the door and into the inside latch operator. An intermediate portion of the spindle is located through a latch assembly which includes a door-latching bolt. Typically, the spindle conforms in cross section to the complementary shape of spindle-receiving openings in the latch operators and in the latch assembly In some instances, the spindle is formed with a square cross section. In other instances, the spindle is formed with a half-round or C-shaped cross section.
Due to the conformity of the cross section of the spindle to the spindle-receiving openings noted above, spindles of one cross section, for example a square cross section, cannot be used with latch operators and latch assemblies having half-round spindle-receiving openings. Therefore, the opportunity to use latch operators having square cross-section spindle openings with latch assemblies having half-round openings is precluded even though this may be desired from time to time in order to match the elements of two such systems into a viable product.
Frequently, door latch products are designed with facility for manually locking the latch assembly from inside the door on which the latch assembly is mounted. Such locking facilities could include a locking dog which is movable into the path of slide which is linked directly to the bolt of the latching assembly. An external pushbutton is coupled to the locking dog for selective positioning of the dog in the path of the slide. An assembly of this type is shown in U.S. Pat. No. 4,296,456 which issued on Oct. 27, 1981. A similar arrangement is illustrated in U.S. Pat. No. 4,142,529 which issued on Mar. 13, 1979.
Such locking dog arrangements require that the dog be located in the vicinity of the latch bolt whereby stress is exerted upon the bolt when an attempt is made to withdraw the bolt by attempted operation of the latch operator.
In view of the foregoing, there is an expressed need for a door latch mechanism which is adaptable to a square spindle drive and a half-round actuator for the latch bolt. Further there is a need for an externally controlled manual locking mechanism which will preclude operation of the latch bolt without directly introducing the locking mechanism into the vicinity of the latch bolt.